Mean peak ASR startle response for gap-prepulse inhibition (gap-PPI) is presented as a function of genotype (HIV-1 Tg or Control; ± SEM). In auditory gap-PPI (a) and visual gap-PPI (b), HIV-1 Tg animals, in comparison to control animals, exhibited a relative insensitivity to the manipulation of interstimulus interval (ISI), evidenced by a flatter ISI function. In tactile gap-PPI (c), a differential sensitivity to the manipulation of ISI was observed. Control animals exhibited peak inhibition at the 30 msec ISI, while HIV-1 Tg animals exhibited peak inhibition at the 50 msec ISI.